<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        * {
            margin: 0;
            padding: 0;
            list-style: none;
        }

        /* 背景样式 */
        .sky {
            width: 100%;
            /* 视窗高度 */
            height: 100vh;
            background: #63aaec;
            animation: sky 10s ease-in-out infinite;
        }

        /* 背景动画 */
        @keyframes sky {
            0% {
                background: #63aaec;
            }

            50% {
                background: black;
            }

            100% {
                background: #63aaec;
            }
        }

        /* 云样式 */
        .sky .cloud1 {
            width: 300%;
            height: 100%;
            background-image: url(./images/cloud_one.png);
            position: fixed;
            top: 0;
            left: 0;
            animation: cloud 20s ease-in-out infinite;
        }

        .sky .cloud2 {
            width: 300%;
            height: 100%;
            background-image: url(./images/cloud_two.png);
            position: fixed;
            top: 0;
            left: 0;
            animation: cloud 25s ease-in-out infinite;
        }

        .sky .cloud3 {
            width: 300%;
            height: 100%;
            background-image: url(./images/cloud_three.png);
            position: fixed;
            top: 0;
            left: 0;
            animation: cloud 30s ease-in-out infinite;
        }

        /* 云动画 */
        @keyframes cloud {
            from {
                left: 0;
            }

            to {
                left: -200%;
            }
        }
    </style>
</head>

<body>
    <div class="sky">
        <div class="cloud1"></div>
        <div class="cloud2"></div>
        <div class="cloud3"></div>
    </div>
</body>

</html>